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Methyl halides are crucial trace greenhouse gases in the atmosphere, playing a significant role in global climate change and the atmospheric environment. This study investigated the photochemical production of methyl halides in an artificial seawater system using guaiacol as a precursor through laboratory simulation experiments. The influences of various environmental factors, including illumination time, radiation wavebands, illumination intensity, concentrations of guaiacol and halide ions (X−), Fe3+, salinity, dissolved oxygen (DO), and pH value on the photochemical production of methyl halides were examined. We demonstrated that increased illumination intensity and duration promote the photochemical production of methyl halides, with a notable enhancement under UV-B radiation. Guaiacol and halide ions were identified as key precursors, and their high concentrations facilitated the formation of methyl halides. Additionally, different types of halide ions exhibited a competitive relationship in producing methyl halides. The study found that an increase in pH inhibited the photochemical formation of CH3I due to the reaction between OH− and ·CH3. Dissolved oxygen was found to inhibit the photochemical formation of CH3I while promoting the formation of CH3Cl. Conversely, an appropriate concentration of Fe3+ enhanced the photochemical production of methyl halides. Field observations indicated a high photochemical production of methyl halides in the natural waters near Qingdao's coastal area, likely due to the high concentration of dissolved organic matter (DOM), which supports photochemical reactions. Furthermore, the photochemical production of methyl halides in natural seawater was significantly higher than in dark conditions, underscoring the importance of illumination in promoting these photochemical processes in seawater. [ABSTRACT FROM AUTHOR]

Carbon monoxide (CO) plays a vital role in the biochemical processes of marine microorganisms, climate regulation, and global carbon cycle. In this study, seasonal and spatial variations of CO and oceanographic factors influencing these variations were investigated in the East China Sea (ECS) during two cruises from 16 to 30 May 2020 and from 8 to 30 October 2021. ECS was as a net source of atmospheric CO in both spring and autumn. The average values of seawater CO concentrations ([CO]surf), atmospheric CO mixing ratio ([CO]atm) and sea‐to‐air flux of CO were 2.22 ± 0.47 nmol L−1 and 0.97 ± 0.86 nmol L−1, 182.8 ± 71.8 ppbv and 102.7 ± 38.8 ppbv, 96.14 ± 25.82 nmol m−2 hr−1 and 31.96 ± 35.61 nmol m−2 hr−1 in spring and autumn, respectively. A steady‐state model was used to estimate the biogeochemical cycling rates of [CO]atm over the ECS. The effect of CO sea‐to‐air fluxes on atmospheric ·OH concentration was likely decreased from spring to autumn. Photoirradiation experiments further showed that the actual contributions of ultraviolet radiation and photosynthetically active radiation to CO photoproduction in the surface waters were 72.2% ± 13.8% and 27.8% ± 13.8%, respectively. The sea‐to‐air fluxes of CO in autumn were 5.15 μmol m−2 day−1 lower than in spring, which were due to larger bacterial consumption and lower [CO]surf in autumn in the ECS. Further, this study is expected to improve our understanding of the biogeochemical processes of CO in the eastern marginal seas of China. Plain Language Summary: Over the past decade, there has been a significant increase in global carbon emissions. CO is a potent greenhouse gas, and chromophoric dissolved organic matter (CDOM) photochemical processes control CO emission from the ocean to the atmosphere. Coastal waters dominate global oceanic carbon emissions, but the dynamics, controls and roles of CO remain largely unconstrained in the marginal seas around China. Here, we conducted a variety of biogeochemical analyses to investigate the controls of CO dynamics cycling in the East China Sea during spring and autumn. [CO]surf, [CO]atm, and sea‐to‐air flux of CO showed significant seasonal variability between spring and autumn, with higher values observed in spring. A variety of environmental factors such as CDOM concentration, wind speed and direction, physical mixing, air‐sea exchange, bacterial consumption, and dark production could affect CO distribution. Compared to air‐sea exchange, bacterial consumption represented the main CO‐sink and contributed over 90% of the total CO loss. These results provide a supplement to the global database of CO cycling processes and improve our current understanding of CO seasonal distribution in coastal ecosystems. Key Points: [CO]surf, [CO]atm, and sea‐to‐air flux of CO in spring were significantly higher than in autumn in the East China SeaThe effect of CO sea‐to‐air fluxes on ·OH was decreased from spring to autumnDark production accounted for about 23% of the total CO production in autumn [ABSTRACT FROM AUTHOR]

Marine isoprene plays a crucial role in the formation of secondary organic aerosol within the remote marine boundary layer. Due to scarce field measurements of oceanic isoprene and limited laboratory‐based studies of isoprene production, assessing the importance of marine isoprene on atmospheric chemistry and climate is challenging. Calculating in‐field isoprene production rates is a crucial step to predict marine isoprene concentrations and the subsequent emissions to the atmosphere. The distribution, sources, and dominant environmental factors of isoprene were determined in the Northwest Pacific Ocean in 2019. The nutrient enrichment in the Kuroshio Oyashio Extension (KOE) surface seawater, driven by the upwelling and atmospheric deposition, promoted the growth of phytoplankton and elevated the isoprene concentration. This was confirmed by observed responses of isoprene to nutrients and aerosol dust additions in a ship‐based incubation experiment, where the isoprene concentrations increased by 70% (t = 4.417, p < 0.001) and 35% (t = 2.387, p < 0.05), respectively. Biogenic isoprene production rates in the deck incubation experiments were positively related to chlorophyll a, temperature, and solar radiation, with an average production of 7.33 ± 4.27 pmol L−1 day−1. Photochemical degradation of dissolved organic matter was likely an abiotic source of isoprene, contributing to approximately 14% of the total production. Driven by high isoprene production and extreme physical disturbance, the KOE showed very high emissions of isoprene of 46.0 ± 13.0 nmol m−2 day−1, which led to a significant influence on the oxidative capacity of the local atmosphere. Key Points: Nutrient enrichment in the surface seawater driven by upwelling and atmospheric deposition promoted the biological production of isoprenePhotochemical production was confirmed as an abiotic source of marine isopreneApproximately 10%∼63% of net isoprene produced in the mixed layer was transferred to the atmosphere [ABSTRACT FROM AUTHOR]

The widespread presence of organic aerosols (OA) in the atmosphere and their dominant role in climate forcing are increasingly recognized. Measurements from the high‐altitude region provide insights into the natural processes and long‐range transport of aerosols. We studied water‐soluble organic compounds in PM1.1 during January‐March 2020 and February‐April 2021 at Ponmudi (8.8°N and 77.1°E), a tropical hill station (960 m a.s.l.) located on the Western Ghats of India. The 5‐day backward trajectories of air masses presented that continental and marine sources impacted the site during the campaign, and thus we classified samples as mixed and marine air masses. Their molecular fingerprints revealed the prevalence of oxalic acid (C2), followed by terephthalic acid in mixed air mass and malonic (C3) or succinic (C4) acid in maritime air mass aerosol samples. This feature and the phthalic to azelaic acid ratio, as well as the C3 to C4 and fumaric to maleic acid ratios, evidenced that water‐soluble OA were of anthropogenic origin and less photochemically aged in mixed air mass samples, whereas they derived from biogenic sources and more photochemical aging in marine air mass samples. However, we found their comparable contributions in water‐soluble organic carbon under mixed and marine air masses. Linear correlations between C2 relative abundance and its ratios with the precursor compounds implied that the oxidation of precursors to oxalic acid occurs during atmospheric transport. The results revealed that the input of anthropogenic and biogenic precursors followed by atmospheric processing controlled the burden of water‐soluble OA across the Western Ghats. Plain Language Summary: Dicarboxylic acids (DCAs), oxocarboxylic acids and dicarbonyls are ubiquitous water‐soluble components of organic aerosol (OA) that can serve as cloud condensation nuclei and affect the climate of the Earth. We reveal for the first time the molecular fingerprints and sources as well as formation processes of water‐soluble OA in PM1.1 at a tropical hill station in Western Ghats of India. Significant differences in the molecular fingerprints and atmospheric processes of water‐soluble OA were found due to the influence of different air masses. DCAs and related compounds in mixed air mass aerosols originated from anthropogenic sources and produced in the atmosphere by photooxidation during long‐range transport whereas they were of biogenic origin followed by intense photochemical aging of biogenic volatile organic compounds such as isoprene and unsaturated fatty acids during atmospheric transport in marine air mass aerosols. The results revealed that DCAs substantially contribute to water‐soluble OA not only in mixed air mass aerosols but also in marine air mass aerosols at the tropical hill station in the Western Ghats. These findings have implications for assessing climate‐forcing feedback of secondary OA over the Western Ghats that is driven by anthropogenic and biogenic sources followed by photochemical processes. Key Points: Mixed and marine air masses drive the molecular fingerprints of atmospheric water‐soluble organic compounds over the Western GhatsAerosols of mixed air masses comprised dicarboxylic acids (DCAs) of anthropogenic origin and less photochemically processedDCAs were produced from biogenic sources followed by intense photochemical aging in marine air mass aerosols [ABSTRACT FROM AUTHOR]

Increasing severe and persistent ozone pollution in China has resulted in serious harm to human health in recent years, yet the precise pollution sources are poorly known because there is few knowledge on large-scale extreme ozone episodes. Here, we studied the formation of the historical orange-alert regional ozone episode in eastern China on 6 June, 2021, by combining process analysis, integrated source apportionment modelling, and chemical and meteorological data. Results show that during the pollution episode, 94% of cities in eastern China suffered ozone pollution, and 39% had daily maximum 8-h average ozone concentrations higher than 100 ppb. This is explained by favorable local ozone formation and transports provided by the prevailing northwestern winds in the upper air, and by sinking atmospheric motions favoring the persistence of high surface ozone concentrations. During daytime, local photochemical production induced an ozone increase of 0.3–28.4 ppb h−1 and vertical transport induced an ozone increase of 0.4–56.1 ppb h−1. As a consequence, vertical downward transport of ozone generated in the upper air by photochemical reactions aggravated surface ozone pollution. Surface ozone concentrations include 25.8–53.9% of ozone from local provincial emissions, 0–42.6% of ozone from inter-regional transports from neighboring regions, 4.6–23.1% of ozone from outer-regional transport, and 13.6–52.9% of ozone from boundary conditions in the selected cities. Overall, our findings show that favorable meteorological conditions promoted the chemical productions of ozone on the surface and at high altitudes, thus resulting in this heavy ozone pollution. In addition, regional and vertical downward transports of aloft ozone further aggravated the surface ozone pollution, leading to the large-scale extreme ozone pollution episode. [ABSTRACT FROM AUTHOR]

The vast rural areas often experience more severe haze pollution than megacities during wintertime in North China Plain (NCP), yet the sources and evolution processes of aerosol particles, particularly organic aerosol (OA) remain poorly understood. Here we conducted real‐time measurements of submicron aerosol (PM1) species using a high‐resolution aerosol mass spectrometer at a representative rural site in NCP in winter 2019. Our results showed the dominance of organics (36%) and nitrate in PM1 (22%) in 2019. Positive matrix factorization analysis illustrated similarly important primary sources from traffic emissions, coal combustion, and biomass burning, yet secondary OA (SOA) from photochemical and aqueous‐phase related processing exceeded primary OA (53% vs. 47%). Substantial decreases in primary species and considerable increases in nitrate and sulphate were observed since winter 2018, demonstrating enhanced secondary formation in winter 2019. OA composition changed significantly from clean period to fog events with the contribution of aqueous phase‐related oxygenated OA increasing from 6% to 44%, while the photochemical SOA decreased correspondingly from 51% to 19%. The size distributions of aerosol species also changed by shifting toward large sizes during fog events. Elemental analysis of OA and the Van Krevelen diagram (H/C vs. O/C) illustrated the different roles of photochemical and aqueous‐phase processing during daytime and nighttime, respectively, and aqueous‐phase processing is subject to the formation of organic compounds with high H/C and O/C ratios. The large differences in fog processing of submicron aerosol species between 2018 and 2019 due to different temperatures were also elucidated. Plain Language Summary: Air quality in megacities in North China Plain (NCP) has been improved significantly during the last decade, however, severe haze pollution events occur frequently in vast rural areas during wintertime. Recent studies have demonstrated stronger health impacts of aerosol particles in rural area than megacities, yet the composition, sources and evolution processes of aerosol particles, particularly organic aerosol (OA) in rural area in NCP remain poorly characterized. Here we have a comprehensive characterization of submicron aerosol species at a rural site in winter in NCP. We observed substantial decreases in primary species and considerable increases in nitrate and sulphate from 2018 to 2019 due to enhanced secondary formation and the decreases in primary emissions. We found similarly important primary sources from traffic emissions, coal combustion, and biomass burning in rural area. However, secondary OA (SOA) from photochemical and aqueous‐phase related processing exceeded primary OA. The aqueous‐phase related SOA increased significantly by up to 44% during fog events, while the photochemical SOA decreased correspondingly from 51% to 19%. The size distributions, elemental composition of OA, and Van Krevelen diagram further illustrated the different roles of photochemical and aqueous‐phase processing in secondary aerosol formation in rural area in NCP. Key Points: Primary organic aerosol (OA) was primarily from coal combustion, biomass burning and traffic emissions in rural North China Plain in winterAqueous phase‐related OA showed large increases during fog events, while photochemical secondary OA was important during non‐fog periodsAerosol composition showed significant changes from 2018 to 2019 due to enhanced secondary formation and changes in primary emissions [ABSTRACT FROM AUTHOR]

In this work, isotopic effects of carbonyls were evaluated during the simulation sampling of gaseous carbonyls by using a carbon isotope method developed, and then variation characteristics of carbon isotopic compositions were investigated for three dominant carbonyls including formaldehyde, acetaldehyde and acetone in the roadside air of Nanning for the first time. A small difference in δ13C values (0.04 to 0.50 ‰) were observed between the calculated and measured values of carbonyl-derivatives, indicating that the effect on carbon isotopic fractionation could hardly occurred in the simulation sampling of gaseous carbonyls. The roadside air measurements showed that δ 13 C values of formaldehyde, acetaldehyde and acetone were –36.02 ‰ to –31.18 ‰, –35.35 ‰ to –32.01 ‰ and –30.45 ‰ to –29.09 ‰, respectively. Further correlation of the measured δ 13 C values was good for formaldehyde, acetaldehyde and acetone (R2 = 0.6275–0.7755), indicating that their similar sources could be the direct vehicular emission or indirect productions from precursors such as hydrocarbons. Particularly, formaldehyde, acetaldehyde and acetone in the roadside air were all enriched in the early afternoon by round 0.5–6 ‰ in 13C compared to other sampling durations, which was likely due to the contributions from the positive photo-oxidation productions of hydrocarbons. Finally, it was found that all measured δ 13 C values (–36.5 ‰ to –29.0 ‰) agreed with the forecasted δ 13 C range (–43.0 ‰ to –26.0 ‰) according to the 13C mass balance of carbonyls and their precursors such as hydrocarbons, indirectly confirming such positive productions in the roadside air. [ABSTRACT FROM AUTHOR]

One of the major goals of the 2005 Antarctic Tropospheric Chemistry Investigation (ANTCI) was to bridge the information gap between current knowledge of South Pole (SP) chemistry and that of the plateau. The former has been extensively studied, but its geographical position on the edge of the plateau makes extrapolating these findings across the plateau problematic. The airborne observations reported here demonstrate that, as at SP, elevated levels of nitric oxide (NO) are a common summertime feature of the plateau. As in earlier studies, planetary boundary layer (PBL) variations were a contributing factor leading to NO fluctuations. Thus, extensive use was made of in situ measurements and models to characterize PBL depths along each flight path and over broader areas of the plateau. Consistent with earlier SP studies that revealed photolysis of nitrate in surface snow as the source of NO x, large vertical gradients in NO were observed over most plateau areas sampled. Similar gradients were also found for the nitrogen species HNO3 and HO2NO2 and for O3. Thus, a common meteorological-chemical feature found was shallow PBLs associated with nitrogen species concentrations that exceeded free tropospheric levels. Collectively, these new results greatly extend the geographical sampling footprint defined by earlier SP studies. In particular, they suggest that previous assessments of the plateau as simply a chemical depository need updating. Although the evidence supporting this position comes in many forms, the fact that net photochemical production of ozone occurs during summer months over extensive areas of the plateau is pivotal.

Methyl iodide (CH3I) is an important trace greenhouse gas in the atmosphere and an ozone-depleting substance. The influence of different environmental factors, such as the duration of illumination; the strength of illumination; the concentrations of humic acid, ferric ion (Fe3+), and iodide ion (I−); and pH, on the photochemical production of CH3I in artificial seawater (ASW) were tested by simulated solar irradiation. In addition, Yangtze River Estuary waters from inshore to offshore were used to explore the relationship between the photochemical production of CH3I and different sources of dissolved organic matter (DOM) in natural sea-water (NSW). The results revealed that higher concentrations of humic acid and I−, as well as higher strengths of illumination and longer illumination durations, promoted the photochemical formation of CH3I in ASW. The addition of Fe3+ accelerated the photochemical production of CH3I, but high concentrations of Fe3+ inhibited the formation of CH3I. Experiments on NSW obtained from the Yangtze River estuary spiked when concentrations of DOM were high, confirming that DOM plays an important role in facilitating the photochemical production of CH3I within the Yangtze River Estuary. The photochemical production of CH3I in the seawater was significantly higher under light conditions relative to dark conditions, indicating that illumination accelerated the production of CH3I. [ABSTRACT FROM AUTHOR]

A comprehensive investigation of ozone, its precursors as well as aerosols in the low troposphere was conducted over the University of Chinese Academy of Sciences site (abbreviated as UCAS site, a northern suburban site) in Beijing during the period of October 26 to November 6, 2014, with a focus on the comparison between polluted and clean conditions. The vertical profiles of ozone and aerosol extinction coefficients in the low troposphere were measured by differential absorption lidar, and the tropospheric vertical column densities (VCDs) as well as vertical profiles of HCHO and NO 2 were measured by ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS). O 3 in the boundary layer (0.3–1.0 km) had a positive gradient with height and presented a stratified structure at night on haze days, in contrast to a uniform distribution during clean episodes. The polluted conditions were characterized by higher levels of atmospheric pollutants (O 3 , aerosol, HCHO and NO 2 ) and more dynamic variations with respect to clean periods. During lightly to moderately polluted periods, elevated concentrations of O 3 within the boundary layer were observed with a maximum exceeding 60 ppbv. In haze days, the air masses from urban Beijing and southern Hebei industrial and urbanized areas could bring large amounts of precursors, enhancing O 3 formation over the lidar site. The photochemical production of O 3 within the boundary layer was controlled by a VOC-limited regime in haze days and turned into a mixed-VOC-NO x -limited regime on clean days. According to sensitivity analysis, when air masses came from southern polluted regions, the sensitivity of ozone production was dominated by VOC-limited regime. The reduction of VOC emissions from urban Beijing and Hebei industrial and urbanized areas would favor the mitigation of O 3 pollution at UCAS site. [ABSTRACT FROM AUTHOR]

Five C 1 -C 4 alkyl nitrates (RONO 2 ) were measured at a coastal site in Hong Kong in four selected months of 2011 and 2012. The total mixing ratios of C 1 -C 4 RONO 2 (Σ 5 RONO 2 ) ranged from 15.4 to 143.7 pptv with an average of 65.9 ± 33.0 pptv. C 3 -C 4 RONO 2 (2-butyl nitrate and 2-propyl nitrate) were the most abundant RONO 2 during the entire sampling period. The mixing ratios of C 3 -C 4 RONO 2 were higher in winter than those in summer, while the ones of methyl nitrate (MeONO 2 ) were higher in summer than those in winter. Source analysis suggests that C 2 -C 4 RONO 2 were mainly derived from photochemical formation along with biomass burning (58.3–71.6%), while ocean was a major contributor to MeONO 2 (53.8%) during the whole sampling period. The photochemical evolution of C 2 -C 4 RONO 2 was investigated, and found to be dominantly produced by the parent hydrocarbon oxidation. The notable enrichment of MeONO 2 over C 3 -C 4 RONO 2 was observed in a summer episode when the air masses originating from the South China Sea (SCS) and MeONO 2 was dominantly derived from oceanic emissions. In order to improve the accuracy of ozone (O 3 ) prediction in coastal environment, the relative contribution of RONO 2 from oceanic emissions versus photochemical formation and their coupling effects on O 3 production should be taken into account in future studies. [ABSTRACT FROM AUTHOR]

A bias in clear-sky conditions that will be involved in estimating particulate matter (PM) concentration from aerosol optical depth (AOD) was examined using PM10 from two Aerosol Robotic Network sites in Korea. The study periods were between 2004 and 2007 at Anmyon and between 2003 and 2011 at Gosan, when both PM10 and AOD were available. Mean PM10 when AOD was available (PMAOD) was higher than that from all PM10 data (PMall) by 5.1 and 9.9 µg/m³ at Anmyon and Gosan, which accounted for 11% and 26% of PMall, respectively. Because of a difference between mean PM10 under daytime clear-sky conditions (PMclear) and PMAOD, the variations in ΔPM10, the difference of PMall from PMclear rather than from PMAOD, were investigated. Although monthly variations in ΔPM10 at the two sites were different, they were positively correlated to those in ΔT, similarly defined as ΔPM10 except for temperature, at both sites. ΔPM10 at Anmyon decreased to a negative value in January due to an influence of the Siberian continental high-pressure system while ΔPM10 at Gosan was high in winter due to an effect of photochemical production at higher temperatures than at Anmyon. [ABSTRACT FROM AUTHOR]

Field measurements of atmospheric carbonyl compounds (carbonyls) and essential precursors of O 3 were carried out in the urban area of Linfen City (Linfen) where serious O 3 pollution has occurred in recent years due to its unique terrain. Carbonyls were sampled using an automatic carbonyl sampler in August 2019 to determine their pollution characteristics and sources. An average concentration of ten carbonyls was 27 ± 5.7 μg m−3 detected using an HPLC-UV system. The concentrations of most detected carbonyls in August were significantly higher than those in the winter months in China. Acetone, formaldehyde and acetaldehyde were the most abundant species, accounting for 73% of all detected carbonyls. Formaldehyde, acetaldehyde, and methacrolein (MACR) were the most significant contributors to OH• reactivity and ozone generation, indicating that these three carbonyls were the key species influencing the production of O 3. The concentrations of formaldehyde, acetaldehyde, and MACR showed similar diurnal variations on most days, with high values during the daytime reaching a peak at 10:00. However, the concentrations of the latter two species varied less than that of formaldehyde during the day. The acetone concentration generally increased continuously from morning to night, with the maximum value around 22:00. The C1/C2 ratio in summer was higher than that in winter. These results indicated that the carbonyls in Linfen were not only affected by anthropogenic sources such as vehicle exhaust but also by secondary photochemical production. The results of formaldehyde source apportionment showed that the contributions of background, primary, and secondary sources to the observed formaldehyde concentration were 27.6%, 36.6%, and 35.8%, respectively. Additionally, this study revealed for the first time that the vertical transport of air masses containing high concentrations of O 3 and NO 3 radicals above the boundary layer could increase the secondary generation of formaldehyde at night in summer. [Display omitted] • Photochemical reactions of carbonyls are important cause for the generation of O 3. • Both photochemical formation and vehicle exhaust contributed carbonyls in summer. • Subsidence of the high-altitude air mass caused secondary formaldehyde increasing. [ABSTRACT FROM AUTHOR]

Photochemical production of carbonyl sulfide (COS), carbon disulfide (CS 2 ) and dimethyl sulfide (DMS) was intensively studied in the water from the Aohai Lake of Beijing city. The lake water was found to be highly supersaturated with COS, CS 2 and DMS, with their initial concentrations of 0.91 ± 0.073 nmol/L, 0.55 ± 0.071 nmol/L and 0.37 ± 0.062 nmol/L, respectively. The evident photochemical production of COS and CS 2 in the lake water under irradiation of 365 nm and 302 nm indicated that photochemical production of them might be the reason for their supersaturation. The similar dependence of wavelength and oxygen for photochemical production of COS, CS 2 and DMS implied that they might be from the same precursors. The water cage effect was found to favor COS production but inhibit CS 2 and DMS formation, indicating that COS photochemical production was mainly from direct degradation of the precursors and the formation of CS 2 and DMS needed intermediates via combination of carbon-centered radicals and sulfur-centered radicals. The above assumptions were further confirmed by simulation experiments with addition of carbonyls and amino acids (cysteine and methionine), and the photochemical formation mechanisms for COS, CS 2 and DMS in water were derived from the investigations. [ABSTRACT FROM AUTHOR]

Understanding the formation of tropospheric ozone (O 3 ) and secondary particulates is essential for controlling secondary pollution in megacities. Intensive observations were conducted to investigate the evolution of O 3 , nitrate (NO 3 − ), sulfate (SO 4 2 − ) and oxygenated organic aerosols ((OOAs), a proxy for secondary organic aerosols) and the interactions between O 3 , NO x oxidation products (NO z ) and OOA in urban Beijing in August 2012. The O 3 concentrations exhibited similar variations at both the urban and urban background sites in Beijing. Regarding the O 3 profile, the O 3 concentrations increased with increasing altitude. The peaks in O 3 on the days exceeding the 1 h or 8 h O 3 standards (polluted days) were substantially wider than those on normal days. Significant increases in the NO z mixing ratio (i.e., NO y - NO x ) were observed between the morning and early afternoon, which were consistent with the increasing oxidant level. A discernable NO 3 − peak was also observed in the morning on the polluted days, and this peak was attributed to vertical mixing and strong photochemical production. In addition, a SO 4 2 − peak at 18:00 was likely caused by a combination of local generation and regional transport. The OOA concentration cycle exhibited two peaks at approximately 10:00 and 19:00. The OOA concentrations were correlated well with SO 4 2 − ([OOA] = 0.55 × [SO 4 2 − ] + 2.1, r 2 = 0.69) because they both originated from secondary transformations that were dependent on the ambient oxidization level and relative humidity. However, the slope between OOA and SO 4 2 − was only 0.35, which was smaller than the slope observed for all of the OOA and SO 4 2 − data, when the RH ranged from 40 to 50%. In addition, a photochemical episode was selected for analysis. The results showed that regional transport played an important role in the evolution of the investigated secondary pollutants. The measured OOA and O x concentrations were well correlated at the daily scale, whereas the hourly OOA and O x concentrations were insignificantly correlated in urban Beijing. The synoptic situation and the differences in the VOC oxidation contributing to O 3 and SOAs may have resulted in the differences among the correlations between OOA and O x at different time scale. We calculated OOA production rates using the photochemical age (defined as –log 10 (NO x /NO y )) in urban plumes. The CO-normalized OOA concentration increased with increasing photochemical age, with production rates ranging from 1.1 to 8.5 μg m − 3 ppm − 1 h − 1 for the plume from the NCP. [ABSTRACT FROM AUTHOR]

The atmospheric global budget and distribution of C 1 –C 3 alkyl nitrates have been investigated using a global three-dimensional chemistry transport model, STOCHEM-CRI. Alkyl nitrates (RONO 2 ) are significant NO x reservoir species and the more detailed VOC oxidation mechanism (CRI v2-R5) leads to greater photochemical production. RONO 2 are significant sources of NO x in regions remote from NO x sources. The study shows that the global burden and the atmospheric life-time of C 1 –C 3 alkyl nitrates are 113 Gg and 9–10 days, respectively, which are in excellent agreement with estimates established by previous studies. The abundance of alkyl nitrates have been found to be higher in the continental atmosphere, with CH 3 ONO 2 mixing ratios up to 20 ppt over the Amazon rainforest. Up to 15, 10, 2, and 5 ppt of modelled CH 3 ONO 2 , C 2 H 5 ONO 2 , n-C 3 H 7 ONO 2 and i-C 3 H 7 ONO 2 have been found in the northern hemisphere over regions with large anthropogenic emissions of NO x and VOCs. The combination of atmospheric production and long-range transport led to high alkyl nitrate levels at high latitudes. The model performance for C 1 –C 3 alkyl nitrates was established using observations from nine flights and nine field campaigns. The comparison shows a tendency towards model under-prediction of the observations, particularly in the southern hemispheric marine boundary layer, possibly due to the absence of oceanic production mechanisms and air-sea exchange processes in the model. The discrepancies between model and observed seasonal cycles, especially of CH 3 ONO 2 , in both hemispheres are discussed. [ABSTRACT FROM AUTHOR]

In this work, the photochemical production of hydroxyl radicals (OH) in suspension of microalgae was studied. Results indicated that algae could induce the photochemical production of OH under UV irradiation, and the production amount of OH increased with increasing concentration of algae. The production of OH induced by algae was strongly pH-dependent, and the suitable pH value for OH production in suspension of algae was 6-7. Moreover, the production amount of OH followed an increasing trend with temperature increasing from 15 to 35 °C. The production amount of OH was greatly enhanced by increasing the irradiation intensity. The algae treated with heat were not benefit to production of OH. Finally, the possible production pathways of OH in suspension of algae were also summarized after analyzing the experimental results and the corresponding references, and the pigments and the dissolved organic matter could initiate the production of excited state of substance which resulted in the production of OH via a series of photochemical reactions involving participation of O2 and H+. [ABSTRACT FROM AUTHOR]

The impact of including a more detailed VOC oxidation scheme (CRI v2-R5) with a multi-generational approach for simulating tropospheric acetone is investigated using a 3-D global model, STOCHEM-CRI. The CRI v2-R5 mechanism contains photochemical production of acetone from monoterpenes which account for 64% (46.8 Tg/yr) of the global acetone sources in STOCHEM-CRI. Both photolysis and oxidation by OH in the troposphere contributes equally (42%, each) and dry deposition contributes 16% of the atmospheric sinks of acetone. The tropospheric life-time and the global burden of acetone are found to be 18 days and 3.5 Tg, respectively, these values being close to those reported in the study of Jacob et al. (2002). A dataset of aircraft campaign measurements are used to evaluate the inclusion of acetone formation from monoterpenes in the CRI v2-R5 mechanism used in STOCHEM-CRI. The overall comparison between measurements and models show that the parameterised approach in STOCHEM-NAM (no acetone formation from monoterpenes) underpredicts the mixing ratios of acetone in the atmosphere. However, using a detailed monoterpene oxidation mechanism forming acetone has brought the STOCHEM-CRI into closer agreement with measurements with an improvement in the vertical simulation of acetone. The annual mean surface distribution of acetone simulated by the STOCHEM-CRI shows a peak over forested regions where there are large biogenic emissions and high levels of photochemical activity. Year-long observations of acetone and methanol at the Mace Head research station in Ireland are compared with the simulated acetone and methanol produced by the STOCHEM-CRI and found to produce good overall agreement between model and measurements. The seasonal variation of model and measured acetone levels at Mace Head, California, New Hampshire and Minnesota show peaks in summer and dips in winter, suggesting that photochemical production may have the strongest effect on its seasonal trend. [ABSTRACT FROM AUTHOR]

Measurements of surface ozone (O), nitrogen oxides (NO = NO + NO), carbon monoxide (CO), and dew point were made at Qinghai Lake (QHL), China, a basin in the remote Tibetan Plateau area, in October 2010 and October 2011. The O mixing ratio was found to be high with average of 41 ± 9 ppb in October 2010 and 57 ± 10 ppb in October 2011. The observed diurnal pattern of O mixing ratio was characterized by a minimum between 07:00 and 10:00 local standard time (LST) increasing ~20 ppb to a broad peak occurring between 13:00 and 18:00 LST. This diurnal pattern differs substantially from that observed at WMO's GAW Baseline Observatory located above the basin on Mount Waliguan, ~130 km southeast of QHL. The elevated O mixing ratios observed in the afternoon are attributed to in situ photochemical production in the air trapped in the QHL basin by surrounding mountains. The low O mixing ratios observed in the morning are most likely due to surface removal in a shallow nocturnal boundary layer. The data indicate substantial impacts of pollution on air quality even in this remote area. The high O values observed in 2011 may cause observable damage to the vegetation, adding stress to an ecosystem ready under the threat of desertification. [ABSTRACT FROM AUTHOR]

Surface O 3 was monitored continuously during Aug. 12, 2010 to Jul. 21, 2011 at a high elevation site (3200 m above sea level) in Qinghai Lake area (36°58′37″N, 99°53′56″E) in Northeast Tibetan Plateau, China. Daily average O 3 ranged from 21.8 ppbv to 65.3 ppbv with an annual average of 41.0 ppbv. Seasonal average of O 3 followed a decreasing order of summer > autumn > spring > winter. Diurnal variations of O 3 showed low concentrations during daytime and high concentrations during late night and early morning. An intensive campaign was also conducted during Aug. 13–31, 2010 to investigate correlations between meteorological or chemical conditions and O 3 . It was found that O 3 was poorly correlated with solar radiation due to the insufficient NO x in the ambient air, thus limiting O 3 formation under strong solar radiation. In contrast, high O 3 levels always coincided with strong winds, suggesting that stratospheric O 3 and long range transport might be the main sources of O 3 in this rural area. Back-trajectory analysis supported this hypothesis and further indicated the transport of air masses from northwest, northeast and southeast directions. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the results of the continuous measurements of surface ozone (O3), oxides of nitrogen (NOx) and methane (CH4) in a rural coastal location at Kannur (11.9°N, 75.4°E, 5m AMSL), India from November 2009 to December 2012. The maximum and minimum mixing ratios of surface O3 were observed in winter and monsoon seasons respectively. NOx concentration was high during mid-night to early morning and low during noontime. The diurnal variations of mixing ratios for NOx and O3 were anti-correlated. Monthly average maximum and minimum CH4 concentrations were observed in December and August respectively. The diurnal variations of CH4 were quite similar to that of NOx. A gradual build up of CH4 was observed during early morning hours of all days throughout the observational period. Further, the analyses of O3, NO, NO2 and NOx have been carried out and the correlation between O3 and its precursors is discussed in detail. The chemical analysis of air samples conducted to identify the main inorganic species present in air and their significance is presented. An attempt has been made to investigate the impact of concentration of Particulate Matter (PM10) present in the ambient air on the production of surface O3 at this location to explore the influence of PM10 on surface O3. [Copyright &y& Elsevier]

Previous measurements of peroxyacetyl nitrate (PAN) in Asian megacities were scarce and mainly conducted for relative short periods in summer. Here, we present and analyze the measurements of PAN, O 3 , NO x , etc., made at an urban site (CMA) in Beijing from 25 January to 22 March 2010. The hourly concentration of PAN averaged 0.70 × 10 −9 mol/mol (0.23 × 10 −9 –3.51 × 10 −9 mol/mol) and was well correlated with that of NO 2 but not O 3 , indicating that the variations of the winter concentrations of PAN and O 3 in urban Beijing are decoupled with each other. Wind conditions and transport of air masses exert very significant impacts on O 3 , PAN, and other species. Air masses arriving at the site originated either from the boundary layer over the highly polluted N-S-W sector or from the free troposphere over the W-N sector. The descending free-tropospheric air was rich in O 3 , with an average PAN/O 3 ratio smaller than 0.031, while the boundary layer air over the polluted sector contained higher levels of PAN and primary pollutants, with an average PAN/O 3 ratio of 0.11. These facts related with transport conditions can well explain the observed PAN-O 3 decoupling. Photochemical production is important to PAN in the winter over Beijing. The concentration of the peroxyacetyl (PA) radical was estimated to be in the range of 0.0014 × 10 −12 –0.0042 × 10 −12 mol/mol. The contributions of the formation reaction and thermal decomposition to PAN's variation were calculated and found to be significant even in the colder period in air over Beijing, with the production exceeding the decomposition. [ABSTRACT FROM AUTHOR]

Ambient formaldehyde, acetaldehyde, and acetone are harmful air pollutants with potential carcinogenic effects on human health. They are considered as important photochemical products from photo-oxidation of atmospheric hydrocarbons. However, little is known on the effet of photodegradation of air pollutants on δC values. Here, we report the first C isotope evidence for the photochemical production of ambient formaldehyde, acetaldehyde, and acetone. Air samples were collected each day during early morning, noon, early afternoon, and late afternoon on 17-19 September 2008 in Guangzhou by drawing air through 2,4-dinitrophenylhydrazine-coated cartridges. The samples were analyzed using high-performance liquid chromatography for concentration analysis and then using gas chromatography-combustion-isotope ratio mass spectrometry for δC analysis. Our results show that ambient formaldehyde, acetaldehyde, and acetone were enriched by 1-5 ‰ in C in the early afternoon relative to other sampling durations, and they also exhibited the highest concentrations in the early afternoon. Measured δC values of formaldehyde, acetaldehyde, and acetone were in the range from −37.15 to −29.01 ‰. The observed enrichment in C implied important photochemical production together with the highest concentrations in the early afternoon. Especially, measured δC range from −37.15 to −29.01 ‰ was in accordance with forecasted δC range from −43 to −28 ‰ based on the mass balance in C between the carbonyls and its major hydrocarbon precursors, providing important C isotope evidence for the photochemical production of ambient formaldehyde, acetaldehyde, and acetone. [ABSTRACT FROM AUTHOR]

This paper aims to apply statistical procedures to analyse the ozone weekend effect (OWE) in three European urban areas: Lisbon, Oporto and London. Seasonal variations of surface ozone (O3) and total oxidant species (Ox) concentrations are presented. The studied period was from January 2007 to December 2009. The O3 annual average profile in London was significantly different from the ones achieved for Lisbon and Oporto, due to the high emissions of nitrogen oxides and low temperatures (associated with low solar radiations). The influence of nitrogen oxides in atmospheric chemistry of London was analysed by linear correlations between O3 concentrations and NO2/NO ratio. High values during almost all period showed that O3 concentrations are mainly influenced by NONO2O3 chemical reaction. On the other hand, the linear correlations between O3 and NO2 concentrations only presented positive values in Lisbon and Oporto. This behaviour is associated with photo-dissociation of NO2, producing O3 during the spring and summer periods. Additionally, cluster analysis was applied to group the days of week according the correspondent O3 behaviour. The weekend and some weekdays (immediately after or before) were grouped in the same cluster, showing that OWE occurs in all urban areas selected in this study. These findings suggest that the applied statistical procedures should be used to analyse the OWE and that the causes for the different O3 behaviours during the week may be influenced by meteorological variables. [ABSTRACT FROM AUTHOR]

Abstract: Formaldehyde and acetaldehyde concentrations over the Eastern half of the United States are simulated with a 3-D air quality model to identify the most important chemical precursors under January and July conditions. We find that both aldehydes primarily result from photochemical production, although 25% or more result from direct emissions in urban areas during winter. Isoprene is the major precursor of formaldehyde in most areas during summer, contributing 20–60% of total production, with the magnitude being spatially variable. Other alkenes from anthropogenic and/or biogenic emissions dominate formaldehyde production in winter, contributing 60–85% of total formation, and are prominent contributors in summer. Alkenes, including biogenic alkenes, dominate acetaldehyde production during both seasons. These conclusions are based on the degradation of emitted VOCs described by the SAPRC07TB chemical mechanism, but even this detailed model has difficulty reproducing observed values better than a factor of 2. The substantial role of isoprene and other alkenes in aldehyde formation emphasizes that we examine and improve emission estimates of these compounds. Until we can estimate the emissions and understand the chemistry of VOC precursors to aldehyde formation with greater certainty, it will be difficult to accurately predict atmospheric concentrations of aldehydes and develop strategies to reduce their concentrations. [Copyright &y& Elsevier]

Abstract: The photochemical characteristics of ozone (O3) and its main precursors (e.g. NOx and VOCs) were investigated in relation to the photochemical O3 budget and O3–NOx–VOC sensitivity, based on a modeling approach using data sets observed during intensive field campaigns conducted under various environmental conditions (i.e. urban (Seoul), rural (Yang Pyeong), landfill (Dae Gu), coastal (Gwang Yang), and remote sites (Jeju Island). The production of O3 under most environmental conditions (especially, spring season at the urban site) was found to be more strongly sensitive to VOCs than NOx. At the landfill site and during summer at the rural and coastal sites, the production of O3 was partially sensitive to NOx. On the other hand, despite the remote air on Jeju Island, the production of O3 was mainly VOC-sensitive (high NOx levels), but in part NOx-sensitive (low NOx levels), due to the transport processes from different environmental regions (e.g. heavily and less polluted locations). [Copyright &y& Elsevier]

Abstract: Continuous measurements of surface ozone (O3) at a semi-arid rural site (14.62°N, 77.65°E) in Anantapur, India during the period from December 2008 to July 2009 are presented. The diurnal variation in O3 shows high concentrations (in the range of 25–77ppbv) during daytime and low concentrations during late evening and early morning hours, due to slower titration of ozone by oxides of nitrogen (NOx). The monthly average high (low) O3 is 56.09±10.1ppbv (27.45±2.3ppbv) at noon in March (July), due to a possible increase in precursor gas concentration by anthropogenic activity and also due to the influence of local meteorological conditions. Furthermore, O3 concentration has been observed as a function of season, which shows that the highest O3 concentration is 52.05±10.2ppbv in the summer and the lowest 30.96±5.7ppbv in the monsoon season. The rate of the increase of surface ozone is high (2.11ppbv/h) in March and low (0.32ppbv/h) in July. Among the meteorological parameters, daily average ozone shows a significantly positive correlation with temperature (R=0.76) and negative correlation with relative humidity (R=−0.62). Throughout the study period, high ozone concentrations were mainly associated with the winds from 150.5° to 260.1°. The weekend ozone effect indicates that higher O3 concentration on weekend compared to weekday suggests that the photochemical production of O3 is non-linear over this site. The results also show that high aerosol concentration has very strong impact on photochemical activities and ozone formation. The correlation between ozone and aerosol concentrations appears in a non-linear feature. Backward trajectory analysis shows that the increase of ozone concentration and the relatively constant high ozone concentrations during the summer might originate from the transport of ozone rich airmass above the boundary layer especially in Northern India and East Asian regions. On the other hand, the airmasses coming from the south over the Indian Ocean contributes low amount of ozone during the monsoon. [Copyright &y& Elsevier]

Abstract: The influence of ship emissions on ozone (O3) concentrations in a coastal area (CA) including Busan port, Korea was examined based on a numerical modeling approach during a high O3 episode. The analysis was performed by two sets of simulation scenarios: (1) with ship emissions (e.g., TOTAL case) and (2) without ship emissions (e.g., BASE case). A process analysis (PA) (the integrated processes rate (IPR) and integrated reaction rate (IRR) analyses) was used to evaluate the relative contributions of individual physical and chemical processes in O3 production in and around the CA (e.g., sites of Dong Sam (DS) and Dae Yeon (DY)). The model study suggested the possibility that pollutant gases emitted from the ships traversing Busan port can exert a direct impact on the O3 concentration levels in the CA. Largest impacts of ship emissions on the O3 concentrations were predicted at the coast (up to 15 ppb) and at inland locations (about 5 ppb) due to both the photochemical production of pollutant gases emitted from the ships and meteorological conditions. From the PA, the photochemical production of O3 (P(O3)) due to ship emissions in the CA was found to increase by a mean of 1.5 ppb h−1 (especially by ≥10 ppb h−1 at the DS site) during the day. [Copyright &y& Elsevier]

Measurement of ambient gas-phase total peroxides was performed at the summit of Mount Tai (Mt. Tai, 1534m above sea level) in central-eastern China during March 22–April 24 and June 16–July 20, 2007. The hourly averaged concentration of peroxides was 0.17ppbv (±0.16ppbv, maximum: 1.28ppbv) and 0.55ppbv (±0.67ppbv, maximum: 3.55ppbv) in the spring and summer campaigns, respectively. The average concentration of peroxides at Mt. Tai, which is in a heavily polluted region, was much lower than hydrogen peroxide measurements made at some rural mountain sites, suggesting that significant removal processes took place in this region. An examination of diurnal variation and a correlation analysis suggest that these removal processes could include chemical suppression of peroxide production due to the scavenging of peroxy and hydroxy radicals by high NOx, wet removal by clouds/fogs rich in dissolved sulfur dioxide which reacts quickly with peroxides, and photolysis. These sinks competed with photochemical sources of peroxides, resulting in different mean concentrations and diurnal pattern of peroxides in the spring and summer. A principal component analysis was conducted to quantify the major processes that influenced the variation of peroxide concentrations. This analysis shows that in the spring photochemical production was an important source of peroxides, and the major sink was scavenging during upslope transport of polluted and humid air from the lower part of the planetary boundary layer (PBL) and wet removal by synoptic scale clouds. During the summer, highly polluted PBL air (with high NOx) was often associated with very low peroxides due to the chemical suppression of HO2 by high NOx and wet-removal by clouds/fogs in this sulfur-rich atmosphere, especially during the daytime. Higher concentrations of peroxides, which often appeared at mid-nighttime, were mainly associated with subsidence of air masses containing relatively lower concentrations of NOy. [Copyright &y& Elsevier]

Abstract: Samples of lake water and coastal seawater from Nova Scotia, Canada, were irradiated with natural or artificial sunlight to investigate the potential for photochemical hydrogen production. Hydrogen photo-production was observed in all natural water samples. Rates of hydrogen formation were highest in coloured lake water (range: 98–163 pmol L−1h−1) and lower in seawater (range: 19–45 pmol L−1 h −1). Dilutions of the most highly coloured lake sample (Kejimkujik Lake) showed a positive linear relationship between H2 production rates and CDOM concentration. Photo-production rates normalised to UV absorption coefficients at 350 nm indicated that the photochemical efficiency of hydrogen formation varied between samples, perhaps due to differences in the CDOM composition. Photochemical hydrogen formation was also seen in solutions of syringic acid and acetaldehyde: two low-molecular-weight carbonyl compounds found in natural waters. Photochemistry may therefore offer least a partial explanation for the persistently high levels of hydrogen observed in the low-latitude surface ocean. [Copyright &y& Elsevier]

Oxalic acid is the dominant dicarboxylic acid (DCA), and it constitutes up to 50% of total atmospheric DCAs, especially in non-urban and marine atmospheres. A significant amount of particulate H2Ox/oxalate (Ox) occurred in the coarse particle fraction of a dichotomous sampler, the ratio of oxalate concentrations in the PM10 to PM2.5 fractions ranged from 1 to 2, with mean±sd being 1.4±0.2. These results suggest that oxalate does not solely originate in the gas phase and condense into particles. Gaseous H2Ox concentrations are much lower than particulate Ox concentrations and are well correlated with HNO3, HCHO, and O3, supporting a photochemical origin. Of special relevance to the Bay Region Atmospheric Chemistry Experiment (BRACE) is the extent of nitrogen deposition in the Tampa Bay estuary. Hydroxyl radical is primarily responsible for the conversion of NO2 to HNO3, the latter being much more easily deposited. Hydroxyl radical is also responsible for the aqueous phase formation of oxalic acid from alkenes. Hence, we propose that an estimate of obtained from H2Ox/Ox production rate and we accordingly show that the product of total oxalate concentration and NO2 concentration approximately predicts the total nitrate concentration during the same period. [Copyright &y& Elsevier]

Abstract: The main purpose of this study was to evaluate the contribution of anthropogenic pollutants to the increase of tropospheric ozone levels in the Oporto Metropolitan Area (Portugal) since the 19th century. The study was based on pre-industrial and recent data series, the results being analyzed according to the atmospheric chemistry. The treatment of ozone and meteorological data was performed by classical statistics and by time-series analysis. It was concluded that in the 19th century the ozone present in the troposphere was not of photochemical origin, being possible to consider the respective concentrations as reference values. For recent data a cycle of 8h for ozone concentrations could be related to traffic. Compared to the 19th century, the current concentrations were 147% higher (252% higher in May) due to the increased photochemical production associated with the increased anthropogenic emissions. [Copyright &y& Elsevier]

Abstract: We report measurement results of ozone (O3) and carbon monoxide (CO) obtained from 5 July to 23 November 2003 at the summit of Mount Tai (1534m a.s.l, 36.25°N, 117.10°E) in the Shandong Peninsula of China. The study was carried out to gain insights into regional O3 pollution and air-mass transport in the highly populated North China (Huabei) Plains. The average mixing ratio was 58 (±16) ppbv for O3 and 393 (±223) ppbv for CO during the study period. The monthly variations in O3 and CO exhibited a similar pattern, i.e. high in summer and low in autumn. While such a seasonal pattern for O3 is a common phenomenon in many rural areas in the Northern Hemisphere and is mainly due to seasonal changes in solar radiation and temperature, the higher CO levels in summer were attributed to the difference in dynamic transport and the evolution of PBL heights in summer and autumn over this region. An examination of diurnal variations in O3 indicated evident daytime photochemical production, especially in summer. The evolution of PBL heights and mountain-valley breezes also had a large impact on the diurnal patterns of O3 and CO. O3 and CO showed a moderately good positive correlation () in July with a slope of 0.08ppbv/ppbv, which is much lower than the slope (0.3–0.4ppbv/ppbv) observed in North America. A back trajectory analysis showed that air masses mainly originated from the North China Plains or were re-circulating over the Shandong Peninsula, collectively accounting for 76% of the air masses sampled. Summertime air traveling in the lower troposphere over northern China had the highest concentrations of O3 and CO, revealing that the lower troposphere in northern China was significantly polluted in summer due to strong convection transporting PBL pollution to the free troposphere. The trajectories also showed notable contributions from eastern China, central China, and countries in northeast Asia such as Korea and Japan. [Copyright &y& Elsevier]